Field of the Invention
The present invention relates generally to resilient seated valves such as butterfly valves and more specifically to valves with resilient seats fastened to the closure member with a retaining ring.
Valves with resilient seats have been commonly used in the water and wastewater systems to control flow in such systems. The nature of the resilient seat allows the valve to provide a zero leakage seal under normal operating conditions. The tight seal is provided by a set interference between the resilient material and the corrosion resistant mating surface. The resilient seal can be located on either the outside diameter of the closure member or the inside of the body shell which will mate against an opposing corrosion resistant sealing surface that can be either an integral part or fastened to the valve.
By its natural properties, a resilient seal will flex and flow under pressure to fill gaps or worn grooves in the mating sealing surface. Because valves when installed are subject to wear and deflection in service, an important feature of resilient seated valves is their ability to be adjusted or replaced in the pipeline or piping system. Butterfly valves having an economical and easily adjustable or replaceable seat are of great value to the owner of the piping system.
One type of resilient seated valve is disclosed in U.S. Pat. No. 3,544,066, wherein the resilient seat is contained in a triangular shaped slot or groove in the valve body. Adjustment is accomplished by injecting an epoxy material behind the seat to deflect the rubber outward toward the sealing surface on the outside diameter of the disc. Such adjustment requires special injection pots, chemicals, needles, and piping. Practice has shown that great skill is needed to make adjustments under field conditions. An improvement in this design is disclosed in U.S. Pat. No. 5,538,029, where a polymeric injection is used from the outside of the valve. Given that the original epoxy is set, a future injection at a later date may be ineffective in moving the resilient seat in the intended direction. In both designs, replacement of the seat requires removal of the old seat with chisels and other sharp objects, followed by a new epoxy injection with a new resilient seat. The materials and equipment to accomplish this task are not readily available and must be purchased or shipped to the job site a great expense and time.
A more practical design, and one which has been commonly employed for many decades is shown in U.S. Pat. No. 4,944,489, where the flexible seat of the valve is secured to the closure member with a retaining ring which is held to the closure member by a circle of threaded fasteners. Another design is illustrated in the American Butterfly Valve literature which shows a solid stainless steel ring intended for corrosive service. The clear practicality of this design is that adjustment or replacement of the seat requires just a simple hand wrench which can be found in any tool box. This method is quite common and used in many valves. However, in water service, the cost of materials, and most specifically the retaining ring, becomes extremely high because of the need for a corrosion resistant alloy such as Type 316 stainless steel. When the retaining ring is fabricated from a plate, the vast majority of the material (that material in the center of the ring) becomes waste. Further, because of the low stiffness of the part due to its shallow thickness, narrow width, and large diameter, extreme care is needed to fabricate the part and maintain the necessary precision. When a large thin ring is machined, internal stresses cause the part to bend or bow when it is removed from the restraint of the mill or lathe. Further thermal processing and straightening processes are often necessary to produce a flat, concentric, and useful part.
Retaining rings have been segmented as disclosed in U.S. Pat. No. 5,377,954. The purpose of these segments is to allow the ring to be assembled into an exterior groove, not to improve the manufacturability of the ring. This ring is likely still made in one large ring and then cut into the segments shown.
There is a need for a ring that provides for easy adjustment and replacement of the resilient seat. The ring must also provide sure and fast retainment of the resilient seat, even under extreme flow rate and pressure conditions. Finally, use has shown that a bolted retainer ring is desirable to achieve these features. However, the difficulties of its manufacture make it cost prohibitive in general water applications. An improved retainer ring must therefore be simple and economical to manufacture while providing the aforementioned performance features.